Remove Black / White Matte

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Photoshop offers a few functions to remove white or black outer edges of an image surrounded by transparency. It can be found in Layer ➔ Matting ➔ Remove Black Matte or Remove White Matte.

The functions are also very useful to fix semi-transparent shadows that were rendered against a white or black background. It removes the white or black sheen from the semi-transparent shadows, making the shadows and rim pixels ready to be placed on any kind of background color or image.

I really miss these options in Affinity Photo, and would be very happy to see them implemented.

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I've tried Erase White Paper on an image with a transparent background, but the filter also makes opaque parts semi-transparent. It's not the same as Photoshop's Remove White / Black Matte, which only removes the white or black residue in anti-aliased edges and the transparent part(s) of an image — such as semi-transparent shadows on a transparent background — effectively preparing it to be overlaid on any other color. That's what I really miss in Affinity Photo.

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I also need something like this, if I'm understanding properly. I'm creating graphics for print on T-shirts. The customer chooses the color of the shirt online. They might pick a dark shirt or a light one, and yet the print has to look nice on it either way.

The direct-to-garment printer prints semi-transparent pixels on a white matte, so these designs will have glowing edges on a dark shirt unless I get rid of the semi-transparent pixels.

I found a way to accomplish this pretty easily for the black color. Fortunately, many of my drawings are outlined in black, making this easy for these cases. The procedure:

Rasterize the document.

Select the "Flood Select Tool" (aka magic wand). Set tolerance to 99%. (Uncheck "contiguous" if I can get away with it.)

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Imo it's just better to render anything against black background to exr output file. With a special shadow catcher material for shadows. Usually 3d soft allow to render "layers", a special set of objects on a black background whatever actual background is. And also capable to output un-premultipled by alpha result so you wouldn't have any black halo at all.

Or you could just divide 32 bit floating point exr alpha channel to premultiplied render getting same un-premultiplied result .

And I even don't mention deep pixel exr and cryptomatte modern 3d soft doing. So having done it in 3d soft properly would make you never using that matte thing